This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-139678, filed May 20, 1999, the entire contents of which are incorporated herein by reference.
This invention relates to a distance-measuring device used in an image pickup device, such as a camera for using a silver-salt film, a digital camera, or a video camera, and more particularly to a distance-measuring device realizing for measuring subject distances at points on the shooting screen (so-called multi-autofocus, hereinafter referred to as multi-AF), characterized by a wide distance-measuring area, such as full-screen AF.
Today, it is becoming quite common for image pickup devices, such as cameras, to implement multi-AF. Cameras equipped with a distance-measuring device for measuring subject distances at three, five, or seven points on the shooting screen are commercially available in low-price models.
The multi-AF is one-dimensional multi-AF where distance-measuring areas are arranged on a straight line. Recently, there have been signs of the commercialization of two-dimensional multi-AF or area AF.
For example, a camera equipped with a distance-measuring device having an area AF function using as many as 45 distance-measuring areas 17 on the finder view 16 has been commercialized and put on the market.
In such conventional multi-AF, complex calculations, such as distance-measuring calculations, must be repeated as many times as the number of distance-measuring areas increases. To improve the time-lag, various inventions have been disclosed.
For example, Jpn. Pat. Appln. KOKAI Publication No. 2-158705 has disclosed the technique for acquiring pieces of subject distance information in a first distance-measuring mode in which the distances to points on the subject are measured roughly, selecting the subject presenting the subject distance corresponding to the shortest distance from the acquired pieces of information, and measuring the distance only to the selected subject with high accuracy in a second distance-measuring mode, thereby improving the time-lag.
Furthermore, Jpn. Pat. Appln. KOKAI Publication No. 63-131019 has disclosed a technique which is based on the assumption that, in active AF, the closest main subject is present at the place where the amount of light reflected from the projected light is the greatest and which omits distance-measuring calculations for parts where the amount of reflected light is small, thereby improving the time-lag.
Since all the conventional AF methods have used active AF, they have improved the time-lag remarkably. When they attempt to perform full-screen AF or the like, however, a set of projecting elements and a set of light-receiving elements cannot avoid becoming very large, which is an obstacle to putting the device to practical use.
In contrast, passive AF would miniaturize the light-receiving elements much more than active AF, causing no obstacle to putting the device to practical use. Thus, passive AF is more suitable for wide-range multi-AF, such as full-screen AF, than active AF.
In this connection, Jpn. Pat. Appln. KOKAI Publication No. 62-103615 has disclosed the technique for performing rough correlation operation on distance-measuring areas, selecting one of the distance-measuring areas on the basis of the result of the operation, and then performing high-accuracy correlation operation on only the selected distance-measuring area, thereby improving the time lag by passive AF.
The rough correlation operation is performed by thinning out sensor data items, such as using every other sensor data item in calculations, but can never be omitted. Thus, although active AF has a higher efficiency of time-lag measures than passive AF, both types of AF produce the same effect.
A recently proposed solution to the problem of which of passive AF and active AF is more suitable for wide-range multi-AF, such as full-screen AF, is a distance-measuring method using hybrid AF. In hybrid AF, which is now in use, a steady-state light removing circuit for removing steady-state light is provided for each light-receiving element in a passive sensor. A passive operation is performed, when the steady-state light removing function is disabled, whereas an active operation is performed when the steady-state light removing function is enabled. Jpn. Pat. Appln. KOKAI Publication No. 10-336921 has disclosed such a steady-state light removing circuit. Products using hybrid AF are already available on the market.
To perform wide-range multi-AF, such as full-screen AF, time-lag measures are essential. For this reason, various devices have been thought out to avoid using high-speed, expensive CPUs and microcomputers at the sacrifice of cost. One of principal devices divides the process of measuring the distance in two: the first half of the process for pre-distance measurement and the second half of the process for actual distance measurement.
The purpose of the pre-distance measurement is to measure the distance roughly in a short time and estimate the position of the main subject, whereas the purpose of the actual distance measurement is to limit time-consuming high-accuracy distance measurement to the necessary-minimum subjects on the basis of the result of the pre-distance measurement in the preceding process. Although the process of short-time pre-distance measurement increases, the time required to measure the distances to the subjects excluded is eliminated, which helps shorten the entire distance-measuring time.
More specifically, in one type of pre-distance measurement, light is projected onto subjects and the position of the main subject is estimated on the basis of the amount of reflected light.
When the position of the main subject is estimated, however, the result might be contrary to the intention of the photographer, or in other words, the result goes against the meaning of the camera shooting mode.
Specifically, there may be a case where the distance to the periphery of the screen is measured, when the spot mode for measuring the distance to the central part of the shooting screen has been set.
It is, accordingly, an object of the present invention to realize without a rise in cost and provide a high-accuracy distance-measuring device and a high-accuracy distance-measuring method which have less time-lag, enable faster operation, and assure a high reliability of the result of distance measurement without ruining the meaning of the camera shooting modes and the like.
According to a first aspect of the present invention, there is provided a distance-measuring device comprising: first distance-measuring means for measuring a subject distance on the basis of a subject image signal produced by a pair of integration-type light-receiving sensors receiving the light from subjects; second distance-measuring means for measuring the subject distance on the basis of an image signal from which steady-state light removing means has removed the steady-state light component from the subject image signal, while projecting means is projecting light onto the subjects; subject select means for causing the second distance-measuring means to operate for a specific time and, according to the image signal obtained from that operation, selecting a subject whose distance is to be measured; mode setting means for setting the operation mode of a camera; and inhibit means for inhibiting the subject select means from operating when the mode setting means has set a specific operation mode.
According to a second aspect of the present invention, there is provided a distance-measuring device comprising: a projecting device for projecting light onto subjects; a light-receiving sensor which is composed of pixels and receives the light from the subjects; a select circuit which operates the projecting device and selects at least one pixel corresponding to a main subject from the pixels according to the output of the light-receiving sensor; a computing circuit for calculating data corresponding to a subject distance from the output signal of the pixel selected by the select circuit; a mode setting circuit capable of setting a normal distance-measuring mode and a spot mode in which distance measurement is made over a narrower range than that in the normal distance-measuring mode; and a control circuit for performing control in such a manner that the pixel is caused to coincide with the spot area corresponding to the narrower range than the normal distance-measuring range, when the mode setting circuit has set the spot mode.
According to a third aspect of the present invention, there is provided a distance-measuring device comprising: a projecting device for projecting light onto subjects; a light-receiving sensor which is composed of pixels and receives the light from the subjects; a select circuit which operates the projecting device and selects at least one pixel corresponding to a main subject from the pixels according to the output of the light-receiving sensor; a computing circuit for calculating data corresponding to a subject distance from the output signal of the pixel selected by the select circuit; a mode setting circuit capable of setting a normal distance-measuring mode and a spot mode in which distance measurement is made over a narrower range than that in the normal distance-measuring mode; and an inhibit circuit for inhibiting the select circuit from operating, when the mode setting circuit has set the spot mode.
According to a fourth aspect of the present invention, there is provided a distance-measuring device comprising: a projecting device for projecting light onto subjects; a light-receiving sensor which is composed of pixels and receives the light from the subjects; a first select circuit which operates the projecting device and selects the one corresponding to a main subject from the pixels according to the output of the light-receiving sensor; a mode setting circuit capable of setting a normal distance-measuring mode and a spot mode in which distance measurement is made over a narrower range than that in the normal distance-measuring mode; a second select circuit for not only inhibiting the first select circuit from operating but also selecting a predetermined pixel, when the mode setting circuit has set the spot mode; and a computing circuit for calculating data corresponding to a subject distance from the output signal of the pixel selected by the second select circuit.
According to a fifth aspect of the present invention, there is provided a distance-measuring method comprising: the step of setting either a normal distance-measuring mode or a spot mode in which distance measurement is made over a narrower range than a normal distance-measuring range; the step of projecting light onto subjects and causing a light-receiving sensor to receive the light from the subjects; the step of selecting at least one pixel corresponding to a main subject from pixels according to the output of the light-receiving sensor, when the normal distance-measuring mode has been set, whereas selecting a predetermined pixel, when the spot mode has been set; and the step of calculating data corresponding to a subject distance from the output signal from the selected pixel.
According to a sixth aspect of the present invention, there is provided a distance-measuring method comprising: a first step of measuring a subject distance on the basis of a subject image signal obtained by receiving the light from subjects; a second step of measuring the subject distance on the basis of an image signal from which the steady-state light component has been removed from the subject image signal, while projecting light onto the subjects; a third step of causing the second step to operate for a specific time and, according to the image signal obtained, selecting a subject whose distance is to be measured; a fourth step of setting the operation mode of a camera; and a fifth step of inhibiting the subject select means from operating, when a specific operation mode has been set.
According to a seventh aspect of the present invention, there is provided a distance-measuring method comprising: the step of projecting light onto subjects; the step of receiving light from the subjects; the step of selecting at least one pixel corresponding to a main subject from pixels according to the output related to the reception of light; the step of calculating data corresponding to a subject distance from the output signal of the selected pixel; the step capable of setting a normal distance-measuring mode and a spot mode in which distance measurement is made over a narrower range than that in the normal distance-measuring mode; and the step of performing control in such a manner that the pixel is caused to coincide with a spot area corresponding to a narrower range than the normal distance-measuring range.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.